Eszopiclone is a cyclopyrrolone that has the chemical name (+)6-(5-chloropyrid-2-yl)-5-(4-methylpiperazin-1-yl)carbonyloxy-7-oxo-6,7-dihydro-5H-pyrrolo[3-4-b]pyrazine or (+)6-(5-chloro-2-pyridinyl)-6,7-dihydro-7-oxo-5H-pyrrolo[3,4-b]pyrazin-5-yl 4-methylpiperazine-1-carboxylate. The chemical structure of eszopiclone is shown below:

Eszopiclone is the S-(+)-optical isomer of the compound zopiclone, which is described in U.S. Pat. Nos. 6,319,926 and 6,444,673, and in Goa and Heel, [Drugs, 32:48-65 (1986)] and in U.S. Pat. Nos. 3,862,149 and 4,220,646. This isomer, which will hereinafter be referred to by its USAN-approved generic name, eszopiclone, includes the optically pure and the substantially optically pure (e.g., 90%, 95% or 99% optical purity) S-(+)-zopiclone isomer.
Zopiclone was the first of a chemically distinct class of hypnotic and anxiolytic compounds that offers a psychotherapeutic profile of efficacy and side effects similar to the benzodiazepines. This class of compounds, the cyclopyrrolones, appears to cause less residual sedation and less slowing of reaction times than the benzodiazepines, and it offers the promise of an improved therapeutic index over benzodiazepines.
The pharmacology of zopiclone has been shown both preclinically and clinically to be characterized by several elements. It is predominantly a hypnotic-sedative, offering significant activity on first treatment without concomitant respiratory or cardiac depression. The compound binds to the benzodiazepine receptor complex, or to a site linked closely to this receptor complex. (See Goa, K. L. and Heel, R. C. Drugs, 32:48-65, (1986); Brun, J. P., Pharmacology, Biochemistry and Behavior, 60 29:831-832, (1988); Julou, L. et al., Pharmacology, Biochemistry and Behavior, 23:653-659, (1985); Verma, A. and Snyder S. H., Ann. Rev. Pharmacol. Toxicol, 29:307-322, (1989). The central benzodiazepine receptor is a macromolecular complex that includes a site for the binding of gamma-aminobutyric acid (GABA), the inhibitory neurotransmitter, suggesting that benzodiazepines and chemically unrelated agonists including zopiclone may exert their effects by facilitating the synaptic effects of GABA. While it interacts with the benzodiazepine receptor, zopiclone apparently has minimal effects on memory, no interaction with alcohol, and little or no abuse or dependence potential. The drug is well absorbed from the stomach, and it is not highly bound to plasma proteins. The racemic mixture, zopiclone, has been in use for some years primarily as a hypnotic, and recently the USFDA approved use of eszopiclone (LUNESTRA™) for the treatment of insomnia.